Initial gain estimation for gamma detector

Abstract

The disclosure presents a process for determining an initial gain of a gamma detector located within a wellbore of a well system. The technique can utilize the subterranean formation characteristics at the gamma detector. The process can sweep, at a step value, across a determined high voltage range. At each sweep step, gamma events can be detected and counted over a detection time interval. The collected gamma events can then be utilized to perform an in-situ plateau test from which a high voltage can be determined, e.g., knee of the plateau curve. The determined high voltage can then be used as the initial gain. Additional fine gain control functions can be executed to further adjust the gain. In an alternative aspect, the collected gamma events can be utilized to perform diagnostics to infer faults or issues with the gamma detector assembly while it is down-hole.

What is claimed is: 
     
       1. A method to determine a gamma detector gain of a gamma detector inserted into a wellbore of a well site, the method comprising:
 determining a high voltage range utilizing the gamma detector and subterranean formation information of the well site; 
 sweeping through the high voltage range utilizing a high voltage step value to determine one or more high voltage data collection points, wherein the high voltage step value is determined by one or more of an approximate distribution of steps across the high voltage range, and a variable distribution of steps utilizing portions of the high voltage range; 
 counting detected gamma events at each high voltage data collection point utilizing the gamma detector, wherein the counting is performed for a detecting time interval prior to adjusting the high voltage data collection point to a subsequent high voltage data collection point utilizing the high voltage step value; and 
 estimating a high voltage knee value utilizing the count of detected gamma events. 
 
     
     
       2. The method as recited in  claim 1 , further comprising:
 setting an initial gain to the high voltage knee value; and 
 executing fine gain control functions utilizing the initial gain to determine the gamma detector gain. 
 
     
     
       3. The method as recited in  claim 1 , further comprising:
 performing a diagnostic analysis of the gamma detector utilizing the high voltage knee value, the detected gamma events, and a pattern of the count of detected gamma events. 
 
     
     
       4. The method as recited in  claim 1 , wherein the subterranean formation information includes a temperature measurement. 
     
     
       5. The method as recited in  claim 1 , wherein the detecting time interval is one or more of a default value, a specified value, and a determined value utilizing the gamma event detection count. 
     
     
       6. The method as recited in  claim 1 , wherein the counting detected gamma events further comprises:
 applying a gamma event threshold and counting detected gamma events that are at or exceed the gamma event threshold. 
 
     
     
       7. The method as recited in  claim 1 , wherein the method is performed at least one of a time when the gamma detector is first lowered into the wellbore, a time when the temperature at a location of the gamma detector changes by a temperature differential value, a time when a re-detection time interval has elapsed, a time when the gamma detector is powered up, a time when a command is received, and a time when the gamma detector attempts to recover from a fault condition. 
     
     
       8. The method as recited in  claim 1 , wherein the sweeping further comprises:
 reducing the high voltage range utilizing at least one of a lookup table, an algorithm, and information from previous executions of the method. 
 
     
     
       9. The method as recited in  claim 1 , wherein the counting is performed by the gamma detector and the method further comprises:
 transmitting the count of detected gamma events to a second system; and 
 performing the estimating at the second system. 
 
     
     
       10. A computer program product having a series of operating instructions stored on a non-transitory computer-readable medium that directs a data processing apparatus when executed thereby to perform operations to determine a gamma detector gain of a gamma detector inserted into a wellbore of a well site, the operations comprising:
 determining a high voltage range utilizing the gamma detector and subterranean formation information of the well site; 
 sweeping through the high voltage range utilizing a high voltage step value to determine one or more high voltage data collection points, wherein the high voltage step value is determined by one or more of an approximate distribution of steps across the high voltage range, and a variable distribution of steps utilizing portions of the high voltage range; 
 counting detected gamma events at each high voltage data collection point utilizing the gamma detector, wherein the counting is performed for a detecting time interval prior to adjusting the high voltage data collection point to a subsequent high voltage data collection point utilizing the high voltage step value; and 
 estimating a high voltage knee value utilizing the count of detected gamma events. 
 
     
     
       11. The computer program product as recited in  claim 10 , the operations further comprising:
 setting an initial gain to the high voltage knee value; and 
 executing fine gain control functions utilizing the initial gain to determine the gamma detector gain. 
 
     
     
       12. The computer program product as recited in  claim 10 , the operations further comprising:
 performing a diagnostic analysis of the gamma detector utilizing the high voltage knee value, the detected gamma events, and a pattern of the count of detected gamma events. 
 
     
     
       13. The computer program product as recited in  claim 10 , wherein the detecting time interval is one or more of a default value, a specified value, and a determined value utilizing the gamma event detection count. 
     
     
       14. The computer program product as recited in  claim 10 , wherein the counting detected gamma events further comprises:
 applying a gamma event threshold and counting detected gamma events that are at or exceed the gamma event threshold. 
 
     
     
       15. The computer program product as recited in  claim 10 , wherein the method is performed at least one of a time when the gamma detector is first lowered into the wellbore, a time when the temperature at a location of the gamma detector changes by a temperature differential value, a time when a re-detection time interval has elapsed, a time when the gamma detector is powered up, a time when a command is received, and a time when the gamma detector attempts to recover from a fault condition. 
     
     
       16. A system to estimate an initial gain of a gamma detector inserted into a wellbore of a well system, comprising:
 a gamma detector, operable to detect gamma events across a specified high voltage range; and 
 a gamma processor, operable to analyze the detected gamma events, to compute an estimated high voltage knee value utilizing a count of the detected gamma events, and to set the initial gain to the high voltage knee value, wherein the count is determined utilizing a high voltage step value determined by one or more of an approximate distribution of steps across the high voltage range, and a variable distribution of steps utilizing portions of the high voltage range. 
 
     
     
       17. The system as recited in  claim 16 , further comprising:
 a gamma detector assembly, operable to include the gamma detector and the gamma processor; and 
 a wellbore assembly, operable to be maneuvered within the wellbore and to provide power to the gamma detector assembly, wherein the gamma detector assembly is included with the wellbore assembly, and where the wellbore assembly is one of a bottom hole assembly or a downhole tool. 
 
     
     
       18. The system as recited in  claim 16 , wherein the gamma processor is a distributed processor that operates over multiple devices or systems. 
     
     
       19. The system as recited in  claim 16 , wherein the gamma processor is further operable to perform diagnostic analysis of the gamma detector using the detected gamma events.